1. Field of the Invention
The present invention relates to an improved process for activating peroxide-based bleaches. In addition, it relates to concentrated bleaching compositions which alone or in combination with other ingredients can be added to an aqueous medium to effect the bleaching of fibrous materials and other bleachable substances over a wide range of temperatures.
2. Description of the Prior Art
Peroxide-based bleaches, such as hydrogen peroxide and perborates, are well known in the art and have been used for a number of years for bleaching textiles, and more recently, in home laundering applications for the bleaching of fabrics which cannot be safely bleached with chlorine-based bleaches because of problems with fiber and color damage. However, for home laundering use such bleaching agents generally have the disadvantage, as compared to chlorine-based bleaches, that their bleaching effectiveness falls off rapidly as the temperature decreases. For example, peroxide-based bleaches ar relatively ineffective at 60.degree.-160.degree. F, which are typical temperatures for home laundering in the United States.
Considerable effort has been devoted over the years to improve the effectiveness of peroxide-based bleaches at lower temperatures. One approach involves catalytic activation with the use of transition metals which decompose hydrogen peroxide to more reactive moieties which accelerate bleaching at lower temperatures. These activators generally must be used in the presence of compounds having suitable sequestering properties to prevent useless decomposition of the hydrogen peroxide. U.S. Pat. No. 2,975,139 to Kauffman et al. and U.S. Pat. No. 3,156,654 to Konecny et al. are representative of this approach. However, despite its technical feasibility, catalytic activation has not found lasting commercial application because of the difficulty in controlling the activation phenomenon under practical conditions, and interference by other chemical substances commonly found in bleach/detergent compositions.
A different approach to activation involves the use of "organic activators" which react with hydrogen peroxide to form peracids, which are relatively strong bleaching agents. A great number of these so-called "organic activators" are described in the prior art and generally comprise compounds having one or more acyl groups. U.S. Pat. No. 2,898,181 to Dithmar et al., for example, discloses certain carboxylic acid amides as activators for perborate bleaching agents. U.S. Pat. No. 3,163,606 to Viveen et al. discloses a variety of diacylated nitrogen containing compounds as activators for active oxygen releasing bleaches. Among the compounds specifically disclosed in this patent are N,N-diacetylcyanamide and the N-diacyldicyanodiamides. U.S. Pat. No. 3,583,924 to Demangeon et al. discloses a four component cleaning composition including a mineral persalt, an organic activator therefore, a water soluble cupric salt and a copper complexing agent. N,N-diacetylcyanamide and the N-diacyldicyanodiamides are also among the activators for the persalts specifically disclosed in this patent. A later issued Dithmar et al. patent, U.S. Pat. No. 2,927,840, discloses that certain organic nitriles are likewise activators for peroxidic compounds. The patent teaches that the best results are obtained with organic nitriles containing a plurality of nitrile groups which are not separated too far from each other.
A further patent, U.S. Pat. No. 3,756,774 to Kirner, discloses that organic nitriles will react with hydrogen peroxide under acidic conditions to form stable peroxy carboximides which can be employed in the bleaching of cellulosic textile materials in place of alkaline hydrogen peroxide solutions stabilized with sodium silicate. Among the various organic nitriles disclosed as being suitable for this purpose are cyanamide and dicyanodiamide. Other patents directed to methods of stabilizing hydrogen peroxide bleach baths without the use of sodium silicate include U.S. Pat. No. 2,820,690 to Feldman and U.S. Pat. No. 3,437,599 to Helmick et al. The Feldman patent discloses the use of magnesium and calcium orthophosphate salts as stabilizers in place of sodium silicate, while the Helmick et al patent discloses the use of alkaline earth metal carbonates for this purpose.
Despite the extensive efforts devoted by those skilled in the art to finding suitable activators for peroxide-based bleaches, there is in the United States today little practical application of this technology.
There are a number of reasons for this. One is that organic activators generally must be used in equimolar proportions with the active oxygen releasing component of the bleach package. Since most organic activators are relatively expensive, this results in the activator contributing significantly to the cost of the bleach formulation, and in many cases makes the product prohibitively expensive relative to competitive hypochlorite bleaches. Also, many prior art organic activators are relatively toxic or have unpleasant odors which render them unsuitable for use in applications such as home laundering.
A further drawback of many known organic activators is that they are unstable in storage and, hence, are not suitable for use in commercial bleach products which are stored over extended periods of time in warehouses or on the supermarket shelf before consumer use.
Copending U.S. application Ser. Nos. 656,464 (now issued as U.S. Pat. No. 4,025,453) and 656,457, both filed Feb. 9, 1976, describe certain novel activators (cyanamide and metal cyanamides) for peroxide-based bleaches which when employed under alkaline conditions provide substantially improved bleaching action, even at relatively low temperatures, and which are relatively inexpensive and do not suffer from the drawbacks of many of the prior art activators. While cyanamide and metal cyanamides under alkaline conditions have proved to be highly effective activators for peroxide-based bleaches over a wide range of concentrations, temperatures, and in the presence of a variety of detergents, the present invention provides a process and compositions for even further enhancing the already outstanding bleaching effectiveness of cyanamide and metal cyanamide-activated systems to levels comparable to chlorine-based bleaches.